A Kenyan court has charged four Somali men with terrorism offences for helping the militants who attacked a Nairobi shopping mall in September.

At least 67 people were killed when Al Shabaab militants raided the Westgate mall, hurling grenades and spraying bullets at shoppers for what they claimed was punishment for Kenya sending troops to Somalia.

"The accused persons carried out a terrorist attack at Westgate shopping mall on September 21 by supporting a terrorist group," the charge sheet read.

The charges include offering support, providing shelter and providing false documents to the gunmen from the Somali Islamist militant group.

The ethnic Somalis, who had no lawyer, were remanded in custody for one week after the prosecution asked for more time for further investigations.

All the gunmen in the Westgate attack - totalling just four, not the dozen that security forces had initially reported - are understood to have died during the four-day siege.

Interpol is assisting Kenya in trying to identify four bodies suspected to be the gunmen, police said last week.

The Kenyan Red Cross has said some 20 people are still missing, and there are fears more bodies could be found in the wreckage of the mall.

Detectives are continuing to investigate a possible link to Norway, with Ndegwa Muhoro, head of Kenya's police criminal investigation department, saying last week that a telephone call was made to the country from the mall during the attack.

A Norwegian citizen of Somali origin is suspected of being one of the attackers, a 23-year-old named in media reports as Hassan Abdi Dhuhulow.

Norway's PST intelligence agency has said it has investigated reports about the possible involvement of a Norwegian of Somali origin in both planning and carrying out the attack, but has declined to comment if Dhuhulow was involved.

In Somalia, efforts continue to target Al Shabaab with a US drone strike killing the extremists' top suicide bomb-maker last week.

The missile strike follows a raid by US Navy SEALS on Somalia's southern port of Barawe in early October that failed to hit its alleged target, a senior Al Shabaab militant leader named Abdulkadir Mohamed Abdulkadir, also known as Ikrima.